1. Field of the Invention
The present invention relates to a lighting device, specifically to a lighting device that guides lights from a light source such as an illumination lamp to lighting areas through a light-guiding device.
2. Description of the Related Art
Most control panels for on-vehicle equipment incorporate a lighting device that illuminates the operation keys on the panels in dark places. In such a lighting device, usually a light-incoming end surface provided on the rear of a light-guiding device made of acrylic resin or the like is faced to a light source such as a lamp, and light-outgoing end surfaces provided on the fronts of the light-guiding device are faced to the lighting areas of the operation keys, so that the outgoing lights from the light source can be guided to the lighting areas through the light-guiding device.
Now, lights from the light source radiate in all directions, and in order to guide the lights efficiently to the lighting areas, it is conceivably advantageous to expand the area of the light-incoming end surface of the light-guiding device, and to shorten the distance from the light source as much as possible. However, using a thick light-guiding device with an enlarged diameter of the end surface will enlarge the light-guiding device and increase the weight thereof as well, which creates a problem that decreases the space-occupancy factor because of the prolonged focal length and extremely deteriorates the facility in handling. In addition, there is a necessity of securing a specific clearance between the light-guiding device and the light source in order that the heat generated by the light source will not melt the light-guiding device. Therefore, in this type of lighting device, a conventional construction is generally adopted which arranges plural light sources to illuminate the lighting areas in a desired brightness because only a slight portion of the lights from the light source can be guided to the lighting areas.
As mentioned above, the conventional lighting device that irradiates the lighting areas in a desired brightness by arranging plural light sources wastes most of the lights from the light source, which is an inefficient construction. Also, the plural light sources have to be mounted at the specific positions, which involves a problem that increases the costs of components and the assembling cost.
Now, there is another technique put forward, in which a curved reflection membrane is provided near the light source, and most of the lights from the light source traveling in a direction diverted from the light-incoming end surface of the light-guiding device are reflected by the reflection membrane to be guided to the end surface. However, since it is difficult to inexpensively manufacture a reflection membrane that is curved in a specified shape, the technique cannot be considered effective in view of achieving reduction in costs.
The present invention has been made in view of the circumstances of the above conventional techniques, and it is an object of the invention to provide a lighting device that efficiently condenses the lights from the light source to a small specific area, and irradiates the lighting areas in a desired brightness at a low cost with a space saved.
In order to accomplish the foregoing object, the lighting device of the invention includes a light source and a light-condensing device placed to face the light source, which is made of a material of high transmittance. The light-condensing device includes a convex lens having a light-incoming plane and a light-outgoing plane that are convexly curved, and annular portions integrally formed on a periphery of the convex lens, whose section is substantially semi-circular and whose dimension of thickness in an axial direction is enlarged toward the outside in a radial direction. And, the lighting device is constructed such that lights from the light source fall on the light-incoming plane of the convex lens and first inner wall surfaces of the annular portions and go out from the light-outgoing plane of the convex lens and second inner wall surfaces of the annular portions toward a specific area.
In the lighting device thus constructed, not only do lights falling on the light-incoming plane of the convex lens from the light source receive a light-condensing effect but also lights falling on the first inner wall surfaces of the annular portions from the light source are reflected on the outer wall surfaces of the annular portions to receive the light-condensing effect; therefore, laying out the light-condensing device in a state that the light-incoming plane and the first inner wall surfaces face the light source permits most of the lights falling on the light-condensing device from the light source to travel to a small specific area through the light-outgoing plane of the convex lens and the second inner wall surfaces of the annular portions. That is, laying out the light-condensing device in the vicinity of the light source will reduce the rate of the lights that are not used for illumination and are wasted, which makes it possible to irradiate the lighting areas in a desired brightness with a limited number of the light source and to save the provision of the reflection membrane separately.
Also in this construction, if portions of the outer wall surfaces of the light-condensing device, which are located on peripheries of the first inner wall surfaces, are formed into tapered planes such that an aperture thereof decreases gradually toward the light source, the lights from the light source passing through the first inner wall surfaces will arrive at the tapered planes with a large angle of incidence. Accordingly, the tapered planes can totally reflect most of the lights, and the lights reflected on the tapered planes can easily travel to reach the small area. Therefore, if there is a slight dislocation in the light-emitting portion of the light source, or if the light-emitting portion is not a point light source as the case with a filament light source, the tapered planes will restrain the lights from leaking out of the outer wall surfaces of the light-condensing device, and also restrain the reflected lights on the outer wall surfaces from diffusing; thus, the lights from the light source can effectively be used for lighting.
The lighting device of the invention will enhance the practical value by providing a construction that makes the lights from the light source travel to the light-incoming end surface of the light-guiding device through the light-condensing device. That is, by providing a construction such that one end surface (light-incoming end surface) of the light-guiding device is disposed at a position that faces the light-outgoing plane of the convex lens, so that the light-condensing device makes the lights from the light source go out to the one end surface, and the other end surfaces (light-outgoing end surfaces) of the light-guiding device are disposed at positions that face the lighting areas, it is possible to make the lights from the light source efficiently travel to the small light-incoming end surface through the light-condensing device. Thereby, it becomes possible to irradiate the lighting areas in a desired brightness without providing plural light sources and a reflection membrane and to prevent the light-guiding device from expanding the size and increasing the weight.